Go Back  PPRuNe Forums > Ground & Other Ops Forums > ATC Issues
Reload this Page >

Wake Turbulence Separation and helicopters

ATC Issues A place where pilots may enter the 'lions den' that is Air Traffic Control in complete safety and find out the answers to all those obscure topics which you always wanted to know the answer to but were afraid to ask.

Wake Turbulence Separation and helicopters

Old 19th Apr 2021, 20:55
  #21 (permalink)  
 
Join Date: Oct 2001
Location: wherever will have me
Posts: 731
Crab, fully acknowledge the issue that you're describing but the requirements for separation are sourced from ICAO and have been reinforced in recent years by research undertaken by the FAA and EUROCONTROL; albeit that research focused on fixed wing.

The CAA did some work on RW wake turbulence a few years ago (which resulted in a minor amendment to the ICAO materials, I think a note was added) but it focused on RW AS generates of wake, not how they react to wake. I believe that there was a plan to do some (UK) research on this aspect a few years ago but the funding application fell through.
whowhenwhy is offline  
Old 20th Apr 2021, 13:55
  #22 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
whowhenwhy - as I mentioned earlier, every helicopter pilot knows the dangers of another helicopter's rotor wash but despite being of similar strength, especially things like S-92 and Merlin, to a large FW, the vortices do not persist and dissipate in a very short distance from the aircraft.

Even if you do encounter the wake of another helicopter, there is no loss of control or stall, it usually just affects your power required briefly.

There seems to be a dearth of evidence or any research to produce such evidence that would lead you to apply a FW safety protocol to a RW aircraft.

As I mentioned, a 3 min hold is complete overkill for a helicopter to transition after a heavy or super FW has rolled or gone around.
crab@SAAvn.co.uk is offline  
Old 20th Apr 2021, 14:32
  #23 (permalink)  
 
Join Date: Mar 2014
Location: Way north
Age: 44
Posts: 473
Originally Posted by [email protected] View Post
I am led to believe that the FAA don't apply wake turbulence separation to helicopters on approach behind a FW.
Originally Posted by [email protected] View Post
As I mentioned, a 3 min hold is complete overkill for a helicopter to transition after a heavy or super FW has rolled or gone around.
ICAO states that ATC doesn't have to establish wake turbulence separation between VFR flights and preceding heavier aircraft, we'll provide the caution, then the separation rests with the pilot. Same as with consequetive IFR flights on visual approach maintaining their own separation.

The 3 minutes hold is again a requirement by the rules, and some countries allow for the pilots to accept separation to a preceding heavier departure (but I think it has been removed in DOC4444?)... there is no standard phraseology for it though, and I've heard people saying that if the pilot just says he is "ready", it means he will take the wake turbulence separation himself.... though I personally don't like that interpretation.
jmmoric is offline  
Old 21st Apr 2021, 11:45
  #24 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
ATC usually provide the recommended spacing for VFR approaches but mandate the time for departures - haven't ever heard of allowing the pilot to make his own decision on a departure.
crab@SAAvn.co.uk is offline  
Old 21st Apr 2021, 12:42
  #25 (permalink)  
 
Join Date: Mar 2014
Location: Way north
Age: 44
Posts: 473
Originally Posted by [email protected] View Post
ATC usually provide the recommended spacing for VFR approaches but mandate the time for departures - haven't ever heard of allowing the pilot to make his own decision on a departure.
You could ask tower if it is an option to take that separation yourself, I don't believe they would ask you first on that one, since you may inadvertently end up putting a pilot in harms way (if they misunderstand the intention)? I don't know about the local rules for wake turbulence separation for VFR where you fly though?
jmmoric is offline  
Old 21st Apr 2021, 17:12
  #26 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
I don't understand why there should be 'local rules' - surely any difference from ICAO procedures would have to be sanctioned nationally by the CAA.

Any controller is going to play by the rules since it is their licence on the line - it is the rules that need clarifying on this matter.

We have a very good relationship with our local ATC but the increase in traffic now many covid restrictions have been lifted has brought the situation into sharper focus.
crab@SAAvn.co.uk is offline  
Old 21st Apr 2021, 20:38
  #27 (permalink)  
 
Join Date: May 2000
Location: SE England
Posts: 625
it is the rules that need clarifying on this matter
The rules are quite clear, any controller should know exactly which rules they’re applying and I would expect any pilot to know what wake turbulence actions they should take. Sometime there is a mismatch between what the pilot is happy with and what the controller is permitted to apply. It’s a pity the rules don’t always match the real world risk and that there are so many variation of rules depending which flight rules, airport or state you fly from.
Dan Dare is offline  
Old 21st Apr 2021, 21:04
  #28 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
The rules are quite clear, any controller should know exactly which rules they’re applying
The rules do not stipulate FW separation to be applied to RW - it is just assumed.
crab@SAAvn.co.uk is offline  
Old 21st Apr 2021, 21:58
  #29 (permalink)  
 
Join Date: Nov 2006
Location: UK
Age: 56
Posts: 180
Originally Posted by [email protected] View Post
The rules do not stipulate FW separation to be applied to RW - it is just assumed.
That's not my understanding; if an aircraft, FW or RW, is allocated a wake turbulence category, then ATC are obligated to apply it, when required to do so.
alfaman is offline  
Old 21st Apr 2021, 22:24
  #30 (permalink)  
 
Join Date: Oct 1999
Location: the dark side
Posts: 948
Originally Posted by [email protected] View Post
The rules do not stipulate FW separation to be applied to RW - it is just assumed.
The wake vortex is based on weight categories used by ATC L light/ S small /M lower and upper medium /H heavy. Each type including helos have a category allocated to them. Eg R44=L S92=S a320 =M etc. There is no distinction between rotary or FW in the application of the MatsPt1 tables S1 Ch3 P13 also section 9k a bit further down from this link.
https://publicapps.caa.co.uk/docs/33...0117928886.pdf
So a controller shall apply those separations, and they are drummed in under training. Also note separation standards required for parallel runways in said documents. Then ask how does that work with a parallel taxiway and a heli taxiing with skids, eg MD’s Robbo’s,...

A controller has to use those separations, so if you’re at an airfield where rotary has to use the runway for departures and the traffic mix is different weight/wake vortex categories, (and speeds), it can be as frustrating for controllers as it is for the engine drivers...

jumpseater is offline  
Old 22nd Apr 2021, 00:44
  #31 (permalink)  
 
Join Date: Dec 2020
Location: Home
Posts: 39
As others have pointed out, the rules (certainly for the UK) are clearly set out in the national procedures manual. It is unfortunate that at aerodromes where RW mix with larger FW operations those procedures do appear to penalise the RW operations, in some cases quite significantly. Sadly, simply being unhappy with that and posting here doesn't change things. But there is a process for changing things, at your home base, at least, if your ATC people support it. Many national procedures can be varied to take account of local conditions and features....if the variations are published in the local Manual of ATS. To get something into the local procedures it will have to be approved by the CAA and I imagine this will require something along the lines of a safety argument showing that the variation is at least as safe as following the 'standard' rules. Whilst this takes some work and effort, if there are benefits to be gained by both RW operators and ATC (and, probably, the airport), maybe it's worth doing. I've no idea how such things are viewed these days, or how practical it is at your base and with your aircraft, but there may be other possibilities which do not require some of the separations to be applied. In the past I recall one airport where RW (although not larger ones) hover/air-taxied from the apron to a designated point in a grass area, from which they transitioned and set course largely as desired. The point was quite specifically not a FATO and was outside the runway strip - no wake turbulence separation is specified and a caution was issued if the aircraft was going to pass behind or through the recent path of another aircraft. Seemed to work OK, I'd go further and say it worked well for everyone, but maybe it's been stopped in the intervening time.
Equivocal is offline  
Old 22nd Apr 2021, 04:52
  #32 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
Thanks for all the replies - I know what the rules say but the whole argument for wake vortex separation is based on FW encounters with it not RW and especially the dangers to a FW with a small wingspan getting trapped in the vortex and losing control.

It doesn't mention the dangers to RW because they don't know if there are, it is all based on FW research.

Rather than do the studies to see exactly what effects a wake vortex has on a RW, it has just been assumed and read across - the MATS manual specifies FW susceptibility but only mentions helicopters as a generator of wake vortex, not a potential victim.

It seems to me that classifying helicopters in the same way as FW is all about their ability to generate wake, not their susceptibility ie a S92 is far more dangerous to a light FW than an R 22 dues to its weight and therefore downwash strength.

I'm not expecting this situation to change because once you apply a safety measure, no matter how pointless, the amount of work to get it removed in our risk-averse world is unlikely to be completed and fought at every turn.

I have written to the CAA but I won't be holding my breath - I will be advised to read MATS and pointed out that the rules are the rules.

Meanwhile I'll just lose time and revenue waiting for an almost non-existent threat to my aircraft to dissipate, even in conditions where it is physically impossible to affect me.
crab@SAAvn.co.uk is offline  
Old 22nd Apr 2021, 16:26
  #33 (permalink)  
 
Join Date: Dec 2020
Location: Home
Posts: 39
Glad you got that off your chest.
Equivocal is offline  
Old 22nd Apr 2021, 16:32
  #34 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
Well I rather hoped that some educated ATC er would point me in the direction of the evidence used to establish these rules with helicopters rather than just pointing out what MATS says.
crab@SAAvn.co.uk is offline  
Old 22nd Apr 2021, 20:39
  #35 (permalink)  
 
Join Date: Sep 2007
Location: UK
Posts: 69
Originally Posted by [email protected] View Post
Well I rather hoped that some educated ATC er would point me in the direction of the evidence used to establish these rules with helicopters rather than just pointing out what MATS says.
If it is a problem at the airport you’re based at maybe try to approach the airport authority and ATC unit. They they may be able to improve their procedures for example providing dedicated areas for helicopters to operate in which are deemed separated for wake turbulence purposes (see Wake turbulence seperation from helipad (less than 760m) to runway) and cross helicopters where they won’t be crossing the flight path of the fixed wing.
callum91 is offline  
Old 23rd Apr 2021, 08:23
  #36 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
Done all that Callum, the geography doesn't lend itself to any areas for circuit arrivals and departures away from FW. We do have manoeuvring areas for ground cushion work but that is it.
crab@SAAvn.co.uk is offline  
Old 23rd Apr 2021, 13:36
  #37 (permalink)  
 
Join Date: Nov 2006
Location: UK
Age: 56
Posts: 180
Originally Posted by [email protected] View Post
Well I rather hoped that some educated ATC er would point me in the direction of the evidence used to establish these rules with helicopters rather than just pointing out what MATS says.
Your original post asked two questions:
1) why apply the same separation criteria, whether it be distance based or time based, between a FW and a RW?

2) what alleviations are allowed to disregard wake turbulence separation when wind conditions - ie strong crosswind away from other traffic - mean the wake cannot possibly persist and be affecting other traffic?

The answers are above, really: 1) because the rules require it; 2) none, because the rules require it.

You're not going to get a response here that helps any more than that, I'm afraid, because it's not within the gift of those posting here to change it. It doesn't matter whether they want to, or not, they don't have the authority. I'd be staggered if any airfield operator was prepared to sign off a safety case that changes any of that, without clear documented evidence from a higher authority, so your best bet would be lobbying via the CAA, & the BHA perhaps.
alfaman is offline  
Old 24th Apr 2021, 09:08
  #38 (permalink)  
Thread Starter
 
Join Date: Apr 2000
Location: EGDC
Posts: 8,527
alfaman - yes, the answers were what I was expecting, I just wanted to know if anyone had any inside knowledge of studies or trials that actually support the rules as they stand.
crab@SAAvn.co.uk is offline  
Old 24th Apr 2021, 17:57
  #39 (permalink)  
 
Join Date: Jan 2001
Location: Deepest darkest Inbredland....
Posts: 571
Originally Posted by [email protected] View Post
alfaman - yes, the answers were what I was expecting, I just wanted to know if anyone had any inside knowledge of studies or trials that actually support the rules as they stand.
The question could also be; Do you know of any studies or trials which prove the rules are not required?
terrain safe is offline  
Old 24th Apr 2021, 18:01
  #40 (permalink)  
 
Join Date: Oct 1999
Location: the dark side
Posts: 948
Originally Posted by [email protected] View Post
alfaman - yes, the answers were what I was expecting, I just wanted to know if anyone had any inside knowledge of studies or trials that actually support the rules as they stand.
I can’t recall hearing of any tests/trials that determined departure separation standards for rotary vs FW. My guess is Rotary and FW were categorised purely by weight in establishing the rules.
If a change were to be proposed, there may be a baseline platform data of military ops, as, as I understand it UK mil aren’t ‘restricted’ in the same manner. How to access that data, if it exists and if it would be considered meaningful are way above my pay grade. But if you wanted a place to start with examples of safe operations, that might be a path to follow.
jumpseater is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.